Recently, in the fields of servers and high-performance computers, optical transmitters that convert electrical signals to optical signals and transmit the optical signals have been used to enable a large amount of data to be transmitted. Optical transmitters that transmit data by using a plurality of channels (multichannel optical transmitters) are known.
FIG. 1 illustrates a block diagram of a multichannel optical transmitter, and crosstalk.
FIG. 1 is a block diagram of a dual channel (channel 1 and channel 2) optical transmitter. For channel 1 of the optical transmitter 10, a driver 11-1 and a vertical-cavity surface-emitting laser (VCSEL) 12-1 are provided; for channel 2, a driver 11-2 and a VCSEL 12-2 are provided. The drivers 11-1 and 11-2 drive the VCSELs 12-1 and 12-2, respectively, and each of the VCSELs 12-1 and 12-2 converts electrical signals input thereto to optical signals to transmit data. As the current consumption of the driver 11-1 grows large, the effects of crosstalk through the ground increase.
There are known hybrid integrated modules that achieve high-speed operations with their simple configurations and shorten manufacturing processes, enabling reduced manufacturing costs.
Examples of the related art are disclosed in Japanese Laid-open Patent Publication No. 2004-119506, Japanese Laid-open Patent Publication No. 10-223788, Japanese Laid-open Patent Publication No. 2016-92303, Japanese Laid-open Patent Publication No. 2012-68539, and so on.
Currently, the pitch between channels is 250 μm, and it is desirable to achieve a higher density pitch in the future. It is also desirable to improve the transmission speed, and the transmission speed is planned to be increased to 56 gigabits per second (Gbps) per channel in the future.
In a multichannel optical transmitter, with the increasing current flowing in a driver because of a narrowed pitch between channels and speed-up, crosstalk through the ground has remarkable effects.
In view of the above, it is desirable to reduce crosstalk between channels.